I'm having trouble getting connected to oracle 10g databases with the latest version of SQL Developer, the original issue I was having I was able to find a lot of help solving. This issue was a message "no ocijdbc11 found", I have since done several different methods to try and remedy this problem. The most recent was suggested in https://kr.forums.oracle.com/forums/thread.jspa?threadID=644299&start=15&tstart=0 and that was to get ahold of the ocijdbc11.dll and copy it into my oracle 10g folder.
Since doing this the error message has changed to:
"Internal Error: Fetch error message failed! Vendor code 17001"
I had the same error. What worked for me was going into Registry Editor and delete the NLS_LANG key, found under HKEY_LOCAL_MACHINE > SOFTWARE > ORACLE_HOME. Then closed and reopened SQL Developer and problem was gone.